A suicide bomber killed at least 12 people outside a court building in Pakistan's capital Islamabad on Tuesday, Interior Minister Mohsin Naqvi said.

The bomber tried to enter the court building on foot, but detonated the device outside, close to a police vehicle, after waiting there for 10 to 15 minutes, Naqvi told reporters at the site.

"We are investigating this incident from different angles. It is not just another bombing. It happened right in Islamabad," the minister said.

Naqvi refrained from casting blame on any militant group. No group immediately claimed responsibility for the explosion, which also wounded at least 27 people, but Pakistan has struggled over the past months with a resurgent Pakistani Taliban.

The blast hit near the entrance of Islamabad district court, which is typically crowded with a large number of litigants.

People covered in blood lay next to a police van, in videos and pictures on local media.